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All of the changes you make in Firefox, like your home page, what toolbars you use, extensions you have installed, saved passwords and your bookmarks, are all stored in a special folder, called a profile. Your profile folder is stored in a separate place from the Firefox program so that, if something ever goes wrong with Firefox, your information will still be there. It also means you can uninstall Firefox without losing your settings and you don't have to reinstall Firefox to clear your information or troubleshoot a problem.

This information is here for reference. You don't have to follow these steps unless you were directed to do so from another article.

Site-specific preferences: The permissions.sqlite and content-prefs.sqlite files store many of your Firefox permissions (for instance, which sites are allowed to display popups) or zoom levels that are set on a site-by-site basis (see Font size and zoom - increase the size of web pages).

Search engines: The search.json.mozlz4 file stores the user-installed search engines that are available in the Firefox Search bar.

Cookies: A cookie is a bit of information stored on your computer by a website you’ve visited. Usually this is something like your site preferences or login status. Cookies are all stored in the cookies.sqlite file.

DOM storage: DOM Storage is designed to provide a larger, more secure, and easier-to-use alternative to storing information in cookies. Information is stored in the webappsstore.sqlite file for websites and in the chromeappsstore.sqlite for about:* pages.

Download actions: The mimeTypes.rdfhandlers.json file stores your preferences that tell Firefox what to do when it comes across a particular type of file. For example, these are the settings that tell Firefox to open a PDF file with Acrobat Reader when you click on it. For more information, see Change what Firefox does when you click on or download a file.

User preferences: The prefs.js file stores customized user preference settings, such as changes you make in Firefox OptionsPreferences
dialogs. The optional user.js file, if one exists, will override any modified preferences.

Working with profiles

The Refresh Firefox feature can fix many issues by restoring Firefox to its factory default state while saving your essential information. Consider using it before going through a lengthy troubleshooting process.